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Flashcards in Physiology - Pancreas & Liver Deck (23):
1

Both the pancreas and liver secrete into the:

- duodenal lumen
- (pancreas secretes pancreatic juice, liver secretes bile)

2

What type of gland tissue does the pancreas have?

- both exocrine and endocrine tissue
- exocrine pancreas is dominant: secretory cells (acini) connect to ducts and empty in the duodenum
- endocrine pancreas is smaller: islets of Langerhaans (insulin and glucagon hormone secretion)

3

What are the two components of pancreatic juice? Which cell type secretes each?

- pancreatic digestive enzymes (secreted by the acinar cells) and an aqueous alkaline solution rich in NaHCO3 (secreted by the duct cells)

4

The 3 Pancreatic Digestive Enzymes

- proteolytic enzymes (protein digestion), pancreatic amylase (carbohydrate digestion), and pancreatic lipase (fat digestion)

5

What are the three pancreatic proteolytic enzymes? How are they activated?

- trypsinogen, chymotrypsinogen, and procarboxpeptidase
- (each attacks a different peptide linkage)
- trypsinogen gets activated into tryspin by enterokinase/enteropeptidase, which is found in the lumen --> trypsin can then go on to activate chymotrypsin, carboxpeptidase, and other trypsin molecules

6

All cells have proteins, so how does the pancreas protect itself from its own proteolytic enzymes?

- 1) the enzyme needed to activate trypsinogen (enterokinase/enteropeptidase) is only found in the duodenal lumen
- 2) the pancreas secretes trypsin inhibitor, blocking any trypsin activity in the pancreas due to spontaneous activation

7

What is the function of pancreatic amylase and pancreatic lipase? Are these enzymes secreted in an active or inactive form? Why?

- pancreatic amylase: converts polysaccharides into maltose (a disaccharide)
- pancreatic lipase: converts triglycerides into monoglycerides and free fatty acids (pancreatic lipase is the ONLY fat digesting enzyme involved in digestion!)
- both are secreted in an active form because the pancreatic cells lack both polysaccharides and triglycerides, and are therefore not in danger

8

The aqueous alkaline solution makes up the largest part of pancreatic juice. Which compound is it rich in? What role does it play in digestion?

- the solution is rich in sodium bicarbonate (NaHCO3)
- it neutralizes the acidic gastric contents as they enter the duodenum; this is necessary to insure proper functioning of the pancreatic enzymes (they don't work well in acidic environments) and also to protect the duodenal mucosa from the acid

9

What regulates pancreatic exocrine secretion?

- secretin increases alkaline solution secretion and CCK increases the enzyme secretion; both are major enterogastric hormones
- these hormones are released when chyme is present in the small intestine (secretin release stimulated by presence of acid, CCK release stimulated by presence of fat and protein)
- (carbohydrates have no effect on CCK release)
- somatostatin decreases pancreatic secretion (is released with excess acidity)

10

10 Liver Functions

- secretion of bile salts to aid in fat digestion and absorption; metabolic processing of carbohydrates, fats, and proteins after their absorption; detoxing wastes, hormones, drugs, and foreign compounds; synthesis of plasma proteins, clotting factors, and angiotensinogen; storing glycogen, fats, iron, copper, and vitamins; activating vitamin D; removing bacteria and old RBCs; secreting thrombopoitein (platelet production), hepcidin (inhibits iron uptake), and growth-factors; producing acute phase proteins for inflammation; and excreting cholesterol and bilirubin

11

What are the specialized residual macrophages of the liver called? Where do they reside?

- Kupffer cells
- they are found in the sinusoids
- (they engulf any bacteria and old RBCs passing through)

12

What connects the portal veins to the central vein in each lobule?

- sinusoids

13

When is bile produced? What determines whether bile enters the duodenal tract or the gallbladder for storage?

- bile is continuously produced by the liver
- the sphincter of Oddi, when closed, prevents bile from entering the GIT, diverting it into the gallbladder (the sphincter opens during digestion)

14

5 Components of Bile

- bile salts, bilirubin, cholesterol, and lecithin (a phospholipid) in an aqueous alkaline fluid

15

How do bile salts aid in the digestion of fats? How about in fat absorption?

- digestion: bile salts exhibit detergent action, breaking up large fat goblets into a liquid emulsion (increases surface area for pancreatic lipase)
- absorption: bile salts promote the formation of micelles

16

What is bilirubin

- the end waste product of breaking down RBCs' heme

17

What role does bile play in excretion?

- bile allows the body to excrete non-water soluble wastes that are unable to be excreted by the kidneys (because they are hydrophobic)

18

Cholerectic Substances

- these are substances that up-regulate bile secretion
- the most potent cholerectic substance is bile salts, themselves

19

Roles of secretin and CCK in bile production/secretion.

- secretin: increases alkaline fluid component of bile
- CCK: increases secretion of pancreatic enzymes, and causes contraction of gallbladder and relaxation of the sphincter of Oddi = bile enters the duodenum

20

The liver is constantly producing bile, so how can the gallbladder store it without filling up?

- the gallbladder actually concentrates the bile by actively transporting salt out (water follows salt = concentrated bile)

21

What are the three zones of the liver? What type of injury is each prone to?

- zone I: periportal zone; contains the portal triad (bile ductule, branch of portal vein, branch of portal artery); affected 1st by viral hepatitis and ingested toxins (cocaine)
- zone II: intermediate zone
- zone III: pericentral vein/centrilobular zone; contains the central vein; affected 1st by ischemia and metabolic toxins

22

What type of blood do the sinusoids contain?

- mixed, but largely deoxygenated, blood; 80% from the central vein and 20% from the hepatic artery

23

Where do ALT and AST originate from? What about GGT and ALP? Where else is ALP produced?

- alanine transaminase (ALT) and aspartate transaminase (AST) originate in the cytoplasm of hepatocytes
- gamma glutamyl transferase (GGT) and alkaline phosphatase (ALP) originate from the bile/canalicular surface of hepatocytes
- ALP is also produced in bone, intestines, and placenta